Bicycles are widely used for transportation and recreation. A typical bicycle includes a rear wheel carried by a frame and a front wheel carried by a fork that, in turn, is rotatably connected to a forward portion of the frame. In particular, a steering tube is connected at its lower end to the fork and extends through a corresponding passageway defined in the forward portion of the frame. An upper portion of the steering tube is connected to a bicycle stem.
The bicycle stem includes a steering tube clamping portion that clamps to the upper end of the steering tube. A body portion inclines forwardly from the steering tube clamping portion and terminates at a handlebar clamping portion. The incline is generally upward for mountain biking and downward for road biking, as desired by the rider. Of course, the medial portion of the handlebar is connected to the handlebar clamping portion of the stem. The rider is thus able to steer the front wheel by turning the handlebar, and also obtain pedaling leverage and maintain balance by pushing and/or pulling on the handlebar.
The stem is important for proper orientation and positioning of the rider relative to the bicycle. In addition, the stem is desirably relatively strong to avoid potentially catastrophic failure, and is also desirably lightweight to reduce the burden on the rider. Mountain or off-road biking can put especially high demands on the strength of the stem. Road bikes may also place high demands on the bicycle stem in terms of both required strength and being relatively lightweight.
The stem also desirably has relatively high torsional stiffness, that is, a resistance to allowing the handlebar to rotate as the rider pushes on one side while pulling on the other, for example. If the torsional stiffness is too low, the rider's energy is more quickly and wastefully depleted. Moreover, if the torsional strength is insufficient the stem may fail.
A widely used type of bicycle stem includes a body portion or body tube and a steering tube clamp connected to an end of the body tube. The steering tube clamp is in the form of a split tube with a vertical slot opposite the body tube. One or typically two bolts or other fasteners are used to secure the steering tube clamping portion together at the vertical slot. Another type of steering tube clamping arrangement is disclosed in U.S. Pat. No. 6,309,135 B1 to Thomson et al. assigned to the assignee of the present invention and the entire contents of which are incorporated herein by reference. This patent also discloses a unique and widely mimicked four-bolt handlebar clamping member cooperating with the handlebar clamping portion of the stem to grip the handlebar. The handlebar clamping portion defines one semicylinder and the handlebar clamping member defines the other semicylinder to define the cylindrical passageway for receiving the handlebar therein.
The four-bolt handlebar clamping arrangement has proven itself to provide high torsional stiffness. The DEUS bicycle stem offered by Raceface Performance Products of New Westminster Canada also has a four-bolt configuration with the mating clamp surfaces being slightly angled.
A number of bicycle stems have a similar handlebar clamp construction with two medially positioned bolts or fasteners instead of the four corner bolts. For example, U.S. Pat. No. 5,509,328 to Lai and Des. 341,801 to McCormack et al., and published application No. 2002/0166406 A1 to Dunlap each show such two-bolt handlebar clamping arrangements for bicycle stems. The EVOLVE model bicycle stem, also from Raceface, also has a two-bolt configuration.
Although the two-bolt handlebar clamping arrangements may be lighter than the four-bolt arrangements, the two-bolt arrangements may not have sufficient resistance to torsional loads applied to the clamp. Accordingly, the rider may fatigue more easily and/or the clamp may tend to fail prematurely.